Antenna



July 31, 1951 J. W. CHRISTENSEN ETAL ANTENNA Filed June 2-1,

INVENTORS JOHN W. CHRISTENSEN ROBERT C. MOYER ATTOFEMEY l atented July31,1951

ANTENNA John W. Christensen, Cedar City, Utah, and Robert C. Moyer,Indianapolis, Ind., assignors to United States of America as representedby the Secretary of War Application June 21, 1946, Serial No. 678,176

v This invention relates to antenna systems for radiation and receptionof high frequency electromagnetic energy. More particularly, the in-'vention relates to a broad band antenna system for radio objectlocating systems such as for azimuth homing of aircraft. In general, andas one ofthe objects, this invention contemplates utilizing a pair ofbroad band dipole antennas mounted in the leading edges of the wings ofan aircraft wherein the antennas have radiation patterns each with alarge forward lobe, high sensitivity at the cross over point of the twopatterns, and a high differential ratio forsmall angles from thecrossover point.

.Another object of the invention is to provide a simple homing antennasystem capable of operating over a frequency range of 2-1 or better, andsuitable for use on high speed aircraft.

It is still another object of the invention to provide an antenna systemdesigned for interchangeability of dipoles to thereby afford coverageover a broad range of frequencies.

For a better understanding of the invention together with other andfurther objects thereof, reference is had to the following descriptiontaken in connection with the accompanying drawing, in which:

Fig. 1 is a broken away perspective view of a portion of an aircraftwing showing one antenna, according to the invention, with its mounting;

Fig. 2 is a longitudinal sectional view, partly broken away, of theantenna. according to the invention; and

Fig. 3 is a diagrammatic view of an aircraft having an antenna,according to the invention, extending from the forward portion of eachwing,

9 Claims. (Cl. 250--33) Eff) and illustrating the approximate radiationpatterns produced by the antennas.

In Fig. 1 there is shown a wing. Ill extending from the fuselage II ofan aircraft. Mounted in the leading edge portion of the wing II] is anantenna l2 including the dipole members I3 and I I, the supportingelement I5 and the mounting members I6 and I1. Preferably antenna I2 ismounted in the leading edge of each of the two Wings of an aircraft andsubstantially equally spaced outwardly from the opposite sides offuselage II as generally indicated in Fig. 3.

As shown in Fig. 2, the antenna I2 comprises the balanced dipole membersI3 and I4 supported in aligned relation in a streamlined head member I8secured to the free end of the supporting element I5 which is ofgenerally tubular construction. The streamlined head member I8 maybe acasting of metallic material having a bore or socket I9 therethroughpreferably disposed at anangle to the axis'of supporting member I5. Toprevent unwanted radiation losses or electrical connection between thedipole members I3 and I4 and the head member I8, a suitable dielectricmaterial 20 is inserted in the bore I9 between the dipole members I3 andI4 respectively and the head member I8. Dielectric material 20 alsoserves to firmly secure dipole members I 3 and M in position.

Energy for exciting dipole members I3 and I4 is fed thereto by means ofa usual type of concentric or coaxial transmission line 2| having aninner conductor 22 and an outer concentric conductor 23, the inner endof which may be connected through a suitable RF connector 24 to a sourceof electromagnetic energy (not shown). Coupled to transmission line 2|is a line balance convertor or balancing feedline transformer devicegenerally designated 25. Balancing device 25 is similar to thatdescribed in the copending application of Clare Driscoll entitledElectrical Apparatus, Serial No. 634,103, filed December 10, 1945, nowPatent No. 2,530,048, granted November 14, 1950. This balancing device25 comprises a conductor 26 which may be a hollow waveguide typetransmission line extending in substantial parallel relation along aportion of the length of line 2| from the outer end thereof. Conductorlines 2| and 26 are preferably enclosed within the supporting element I5which is in the form of a tubular sleeve or shield to prevent radiationand transmission losses. The end remote from the dipole of conductor 2|is electrically connected as by a shorting bar 21 to the outer conductor23 and the inner conductor 22 is electrically connected'to the conductorline 26 at the end nearer the dipole such as by bending the innerconductor 22 outwardly through an aperture 28 in outer conductor 23 andsecuring the end of inner conductor 22 as by soldering to the conductorline 26 near the outer end thereof as at 26' or by means of a strapmember connecting the outer end of inner conductor 22 to the outer endof conductor 26. The dipole members I3 and I4 are connected to the outerends of conductor lines 2| and 26 respectively, dipole member I3 beingconnected to the outer conductor 23 and dipole It being connectedthrough conductor 26 to the inner conductor 22. To facilitate connectionof dipoles I3 and I4 to conductors 2| and 26, the ends of the latter areeach provided with or formed as plug elements 29 adapted to fit snuglywithin apertures or sockets 30 provided in and near the inner ends ofdipole members 13 and I4. This arrangement also facilitatesinterchangeability of the dipole members It and M for differentfrequencies of operation as desired, and also provides for ease ofassembly and service of the dipole members or arms 13 and M.

The length a: of transformer or balancing device 25 from the shortingbar 2? to the connections to the dipoles l3 and I4 is preferably eithera substantial fraction of or slightly more than a quarter wavelength ofthe center frequency at the desired frequency range of operation. Thelength 1/ of each dipole member 13 and I4 should be greater than aquarter wavelength at this middle frequency of operation when the lengthx is less than a quarter wavelength or the dimension 1 should be lessthan a quarter Wavelength when the length .r is greater than a quarterwavelength. Thus, it will be understood that the balanced antennacomprises the two substantially identical dipole members or arms l3 andl lwhich are adapted to be energized with equal and opposite voltages,the device 25 being adapted to transform the feeding concentric linewhich is normally unbalanced into a balanced line whereby the impedanceof the feedline is matched to that of the dipoles and thereby affordingoperation over a wider band of frequencies than heretofore obtainable.

As hereinbefore described, dipole members or arms is and M are inaligned position and their common axis is preferably angularly relatedto the axis of the supporting tubular member i5, the latter beingsubstantially, perpendicular to the leading edge of the wing Iii. Thedipole members l3 and 14 preferably lie within the central horizontalplane of the wing l8. Thus, the common axis of the dipole members [3 andM is at an angle, preferably of substantially 30, to the leading edge ofwing in, the dipole member [4 extending towards the wing tip beingcloser to the leading edge of wing l9 at a distance d and the outer endof dipole member is (the end nearest fuselage H) being at a greaterdistance d" from the leading edge of wing Hi. It is important that theposition of the antenna l2 relative to the portions of the aircraft beproperly determined in order that the desired function of the antennasmay be achieved. Thus, it is desirable that the dimension D representingthe distance from the fuselage to the point of mounting of thesupporting element I in the wing it], the distance d from the leadingedge of the wing If! to the end of head member l8 and the distance d becalculated accurately in order that the combined radiation patterns ofeach of the two antenna elements mounted in the wings H) of the aircraftmay have the desired high sensitivity at the cross-over point C.

Antenna i2 is held in position in wing In by any suitable means. Onemeans is shown in Fig. 1 where a metallic plate member i6 is shaped tofit the inner surface of the leading edge of wing H). Plate is has abearing aperture at therethrough adapted'to receive in a snug slidablefit the supporting element I5, a suitable aperture in the wing surfacepermitting entry of element I5. On an inner partition SI of wing H! issecured a terminal bracket or socket member I? havin a forwardlydisposed extension 32 and bore 33 through the extension 32 and bracketi! for slidably receiving the element 15. Suitable clamping means suchas clamps 34 and 35 may be associated with or secured to the mountingplate and bracket member I6 and IT for securing supporting element l5against displacement which clamping means, when loosened, permitslidable movement inwardly and outwardly of element I5 to thereby permitadjustment of the dimension d. If desired a closable opening 38 may beprovided in the surface of wing :0 to allow access to the mountingmembers it and H. This arrangement also permitsof removal andinterchangeability of the antennas E2.

The principle of a homing antenna is illustrated by the radiation orfield pattern shown in Fig. 3 which is a horizontal pattern ofsensitivity as obtained when the aircraft is in level flight. Thepattern of Fig. 3 is typical of operation at frequencies near the centerof the frequency range of the antenna system. Such patterns aredependent both on the mounting position of the aircraft and on thecharacteristics of the antenna, not merely on the antennacharacteristics alone. In general, three factors combine to produce themost desirable results; (1) the antenna balance, (2) the spacing andangular position in front of the wing ill, as indicated by the distances(1' and d, and (3) the'distance from the fuselage II (the distance D).

The dipole members 13 and I l function as normal dipole antennas and arepreferably designed to. provide radiation patterns with large forwardlobes. The position of'each pair of dipoles is and M with respect toftheleading edges of wing is and the nose of the aircraft produce twoforward lobes A and B for the left and right antenna l2, respectively.The wing it behind each antenna l2 acts as a reflector thus increasingthe forward sensitivity and it also shields the antenna from signalsources from the rear thus minimizing the back'lobes of the radiationpatterns. Thus, the backward energy is reflected by the antenna and isreturned to reinforce the forward lobes. Due to the fairly close spacingbetween dipoles l3 and I4 and wing H3, win ll] acts as a suitablereflector over a wide range of frequencies. As a result of the combinedeffect, in the plane of the antenna and the wing, of forward lobes, andthe reflection from the wings, a front to back ratio of 20 to 251110 isobtainable and a forward gain of approximately 2' to 1 in voltage overthat of a dipole antenna in free space is realized. Displacement of theforward lobes A and B to the left and right respectively from thecenterline of the aircraft is due to the combined effect of the sweepback angle of. the wings to, the nose of the aircraft and the angularposition of the dipoles I3 and 14 relative to the wing 10. The fact thata signal fromsome. source ahead of the aircraft will produce unequalamplitudes of signal input from each of the antennas 12 except when thatsignal source is dead ahead is utilized in the present invention. Anapproach indicator for a pointer operable from the signals received bythe antennas may be utilized to give an indication of the signal source.This pointer may be moveable to therightor left to correspond to theantenna [2 which produces th stronger, signal input; As theaircraft'direction is changed to balance the pointer, the heading of theaircraft directs the cross-over point 'qof the radiation patterns at thesignal source. The antenna system according to the present invention isadapted to provide an accuracy of or 2 3 over most-of the normalfrequency range; that is, the cross over point C which is shown in Fig.3 as exactly, on the centerline of the aircraft may be 3 to5 01f.

,the centerline nearthe extremes of the frequency tain information by asignal strength meter responsive to the signals received by theantennas. The forward to backward ratio of sensitivity as hereinbeforementioned is in the order of to db., thus making the discriminationbetween forward and rear direction possible as the aircraft follows aparticular course, including a circle course; l H While the antennasystem as hereinbefore described is utilized fundamentally as anindicator of azimuth direction only, it is possible to obtain a roughindication of elevation by putting the aircraft into a 45 position inflight while maintaining proper direction. A 45 clock-wise roll whileheading in the course will produce a right deflection of the pointer ifthe source is at a lower elevation, or a left deflection if the sourceis above the aircraft.

While there has been described what is at present considered thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention.

What is claimed is:

1. A broad band antenna system for airborne radio object-locatingsystems comprising, in combination, an antenna mounted on the leadingedge portion of each of two wings of an aircraft, each antenna beingsubstantially equally spaced from opposite sides of the aircraftfuselage, each antenna comprising a tubular supporting member mounted inthe leading edge of a wing and projecting forwardly and substantiallyperpen- 40 dicularly of said wing, a streamlined head member secured tothe free end of said supporting member, a pair of aligned dipole arms ofsubstantially equal length and each having one end secured within saidhead member with the dipole arms substantially lying in the plane ofsaid supporting member and said leading edge, a coaxial conductortransmission line mounted in said tubular supporting member, one end ofwhich is adapted to be connected to a source of electromagnetic energy,said dipole arms being electrically connected to the opposite end ofsaid transmission line, one dipole arm being connected to the outerconductor and the other dipole arm being connected to the innerconductor, a transformer device comprising a hollow cylindrical membermounted within said tubular member coupled to and in substantiallyparallel relation with said transmission line, said device being adaptedto transform the transmission line which is normally electricallyunbalanced to a balanced line whereby said dipole arms are energizedwith equal and opposite voltages, each of said antennas thus beingadapted to radiate energy with a large forward radiation pattern lobe,the positions of said antennas relative said wings and said fuselagebeing so determined that said two lobes overlap and have a cross-overpoint substantially on the centerline of said aircraft with highsensitivity at said cross-over point and a high difierential ratio forsmall angles from said cross-over point.

2. An antenna system as claimed in claim 1 wherein each pair of dipolearms are disposed at an acute angle relative to said leading edge withthe dipole arm extending toward the wing tip being closer to saidleading edge thansaid other dipolearm. 1 1

3.,An antenna system as claimed in claim 1 wherein the supportingelements of each said an- 5 tenna are adapted to be removeable fromtheir mountings in said wings and wherein said dipole arms areremoveable from connection in said head melnber and from saidtransmission line thereby permitting interchangeability of said antennas-1 and said. dipole arms to afford operation .of said antenna systemover a wide range of frequencies. 4. An antenna system as claimedinclaim 1 wherein each said supporting element is slidably mounted in saidwing whereby the distance of 5 .said head member and said dipole arms infront of said leading edge is adjustable, means being provided forsecuring said supporting element in adjusted position. i 5. In anantenna system for airborne radio 0 object-locating systems, an antennamounted on each of the wings of an aircraft at substantially equaldistances from opposite sides of-the aircraftfuselage, each said antennacomprising a tubular supporting member having one end 5 mounted in theleading edge portion of said wing, a head member secured to the oppositeend of said supporting member, a pair of aligned sockets in said headmember, a dipole arm having one end mounted in each said socket, saiddipoles lying substantially in the central plane of said wing which isparallel to the flat dimension thereof, a coaxial conductor transmissionline mounted in said supporting member having one end adapted to beconnected to a source of electromagnetic energy and its opposite endelectrically connected with said dipole arms, an impedance matchingdevice coupled to said transmission line for matching the impedance ofsaid transmission line to that of said dipole arms, said leading edgeportions of said wings acting as reflectors for energy radiated backwardby said dipoles whereby said backwardly directed energy is reflected toreinforce the forwardly directed energy to provide large forwardradiation pattern lobes, thereby affording high sensitivity at thecross-over points of the forward lobes radiated by each of said twoantennas and affording a high forward gain.

6. In an antenna system for airborne radio object-locating systems, apair of antennas mounted in the leading edge portions of the twoopposite wings of an aircraft and equally spaced from opposite sides ofthe fuselage of said aircraft, each said antenna comprising a pair ofaligned balanced dipole members, means for mounting and supporting saiddipole members of each antenna at the same acute angle with respect tothe leading edge of the wing on which said antenna is mounted, thedipole arm extending toward the wing tip being closer to said leadingedge than the other dipole arm, means for feeding electromagnetic energyto said dipole members, and means for electrically balancing saidfeeding means to said dipole members, the positions of said antennasrelative to said wings and said fuselage being so determined that thelobes of said pair of antennas overlap and have a crossover pointsubstantially on the centerline of said aircraft with high sensitivityat said cross-over point and a high differential ratio for small anglesfrom said cross-over point.

7. An antenna system comprising a pair of spaced dipole antennas, meansfor mounting said antennas in the leading edge portions of the two wingsof an aircraft at substantially equal dis- '7 tances from opposite.sides of the aircraft fuselage, means for mounting the dipoles-of'saidantennas at the same acute angle with respect to said-leading-edgeportions and at an obtuse angle with respect to each other, means forfeeding energy to said antennas, and means for positioning said antennaswith respect to said fuselage to radiate energy with large forwardlobes, the lobes being in one plane and overlapping to provide across-over point substantially on a line perpendicular to the center ofa line connecting said antennas.

8. An antenna system as claimed in claim 6 whereinsaidacuteangle issubstantially 30;

9. A spaced dipole antenna structure comprising a tubular supportingmember, a head member removably mounted on said supporting 1 member, acoaxial transmission line within said supporting member, a hollowconductor within said supporting member-and parallel to said coaxialline,

the endsextending toward said head member of said hollow conductor andsaid coaxial line being-formedasp1ugs, an'aperturein the outer con-'ductor of said coaxial line close to the plug end REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PATENTS Number Name, Date 2,217,321 Runge et a1. Oct. 8',1940 2,258,953 Higgins Oct. 14, 1941 2,259,628 Fener Oct. 21, 19412,403,622 Tuska July 9,1946 2,403,625 Wolff July 9,1946 2,414,266Lindenblad Jan. 14, 1947

